Electroplated AU for conformal coating of high aspect ratio silicon structures

ABSTRACT

A method for electroplating a nonmetallic grating including providing a nonmetallic grating; performing an atomic layer deposition (ALD) reaction to form a seed layer on the nonmetallic grating; and electroplating a metallic layer on the seed layer such that the metallic layer uniformly and conformally coats the nonmetallic grating. An apparatus including a silicon substrate having gratings with an aspect-ratio of at least 20:1; a atomic layer deposition (ALD) seed layer formed on the gratings; and an electroplated metallic layer formed on the seed layer, wherein the electroplated metallic layer uniformly and conformally coats the gratings.

GOVERNMENT RIGHTS

This invention was developed under Contract DE-AC04-94AL85000 betweenSandia Corporation and the U.S. Department of Energy. The U.S.Government has certain rights in this invention.

FIELD OF THE INVENTION

The present invention relates in general to coating structures, morespecifically, electroplating high aspect ratio silicon structures withgold. Other embodiments are also described and claimed.

BACKGROUND

New gratings based on phase contrast imaging techniques have beendeveloped to extend the capabilities of x-ray imaging. Radiography hasbeen utilized for over a hundred years, however, the use of gratingsbased on phase contrast imaging techniques now allows for the detectionof phase shifts in addition to absorption. The gratings must be fineenough in pitch to avoid limiting special resolution, and thick enoughto absorb x-rays. To meet these criteria, the gratings must be formed orcoated with a high x-ray absorbing material at high aspect ratios makingthe fabrication process challenging. Various processes have been used tofabricate such gratings. One such process is the use of a traditionalLIGA process to form gold gratings. The LIGA process uses x-raylithography to obtain polymer structures with vertical and extremelysmooth sidewalls to form gold gratings. Gold gratings made by the LIGAprocess are functional and structurally rigid, however, LIGA processesare costly and time consuming. Another process utilizes reactive-ionetching (RIE) of silicon to generate high aspect-ratio trenches, forexample 1 micron wide and 25-35 microns tall on a 4 micron pitch. RIE ofsilicon allows for precise and repeatable fabrication of substrates thatare transparent to x-rays. The trenches are then coated with a 1 micronthick high density metal creating a 50% duty 1 micron wide, 25-35 microntall grating. The coating of high aspect-ratio trenches tends to collectat the top of the grating and thin towards the base of the grating dueto the depth of the trench. Thus, the resulting layer is neither uniformin thickness nor conformal to the shape of the grating.

SUMMARY

An embodiment of the invention includes a process for pulseelectroplating thick and conformal metal coatings on high aspect-ratiostructures, such as silicon x-ray gratings for phase contrast imaging(PCI). Representatively, in one embodiment, the process includesproviding a nonmetallic grating and performing an atomic layerdeposition (ALD) reaction to form a seed layer on the nonmetallicgrating. The process may further include electroplating a metallic layeron the seed layer such that the metallic layer uniformly and conformallycoats the nonmetallic grating. The nonmetallic grating may be a highaspect-ratio grating, for example, a grating having an aspect-ratio ofgreater than 20:1, for example, at least 26:1 or at least 50:1. In oneembodiment, the seed layer may be a platinum layer and the metalliclayer may be a gold layer.

An embodiment of the invention may further include an apparatusincluding a silicon substrate having gratings with an aspect-ratio of atleast 20:1. An atomic layer deposition (ALD) seed layer may be formed onthe gratings and an electroplated metallic layer may be formed on theseed layer. The electroplated metallic layer may be formed in such amanner that it uniformly and conformally coats the gratings.

The above summary does not include an exhaustive list of all aspects ofthe present invention. It is contemplated that the invention includesall devices, systems and methods that can be practiced from all suitablecombinations of the various aspects summarized above, as well as thosedisclosed in the Detailed Description below and particularly pointed outin the claims filed with the application. Such combinations haveparticular advantages not specifically recited in the above summary.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments of the invention are illustrated by way of example andnot by way of limitation in the figures of the accompanying drawings inwhich like references indicate similar elements. It should be noted thatreferences to “an” or “one” embodiment of the invention in thisdisclosure are not necessarily to the same embodiment, and they mean atleast one.

FIG. 1 shows a cross-sectional side view of one embodiment of a grating.

FIG. 2 shows an illustrative process for manufacturing an electroplatedgrating according to one embodiment.

FIG. 3 shows a schematic cross-sectional view of one embodiment of anatomic layer deposition reactor with a back purge feature enabled.

FIG. 4 shows a schematic cross-sectional view of the atomic layerdeposition reactor of FIG. 3 with the back purge feature disabled.

FIG. 5 shows a schematic top view of one embodiment of an electroplatingchamber used to manufacture an electroplated grating.

FIG. 6 shows a schematic of a portion of the solution inlet of theelectroplating chamber of FIG. 5 along line 5-5′.

DETAILED DESCRIPTION

In this section we shall explain several preferred embodiments of thisinvention with reference to the appended drawings. Whenever the shapes,relative positions and other aspects of the parts described in theembodiments are not clearly defined, the scope of the invention is notlimited only to the parts shown, which are meant merely for the purposeof illustration. Also, while numerous details are set forth, it isunderstood that some embodiments of the invention may be practicedwithout these details. In other instances, well-known structures andtechniques have not been shown in detail so as not to obscure theunderstanding of this description.

FIG. 1 shows a cross-sectional side view of one embodiment of anelectroplated grating. Grating 100 may be formed by a collection ofregularly spaced, parallel, elongated elements 102A, 102B, 102C (e.g.gratings), which are separated by trenches 104A, 104B. In oneembodiment, grating 100 may be a nonmetallic grating formed from anonmetallic substrate. Representatively, grating 100 may be a silicongrating formed by a deep reactive-ion etching (DRIE) process such thatgrating 100 is a high aspect-ratio grating. In other words, the depth(d) of elongated elements 102A-102C is much greater than their width(w). Representatively, in one embodiment, grating 100 may have anaspect-ratio of at least 20:1, at least 26:1, at least 50:1 or fromabout 20:1 to about 60:1, or from 26:1 to 50:1. Representatively, thedepth (d) of each of elongated elements 102A-102C may be from about 20microns to about 60 microns, for example, from about 26 microns to about50 microns. The width (w) of each of elongated elements 102A-102C may befrom about 0.5 microns to about 1.5 microns, for example, 1 micron. Inaddition, a pitch (p), or spacing between each of elongated elements102A-102C may be from about 1 micron to about 5 microns, for example,from about 2 microns to about 4 microns, or 3 microns.

As previously discussed, in order for grating 100 to be suitable for usein optics applications, such as x-ray imaging, grating 100 must includea metallic x-ray absorbing material, for example, gold. Thus, inembodiments where grating 100 is a DRIE silicon grating, it must becoated with the x-ray absorbing material. Grating 100, however, is firstcoated with a seed layer 106 followed by a metallic layer 108. The seedlayer 106 facilitates coating of grating 100 with the metallic layer108, as will be discussed in more detail below.

In one embodiment, seed layer 106 may be made of a metallic materialcapable of uniformly and conformally coating grating 100. In otherwords, a thickness (t1) of seed layer 106 is the same along the entiresurface of grating 100 and the profile of grating 100 remainssubstantially the same after application of seed layer 106. In oneembodiment, seed layer 106 may be a platinum layer or any conductingmaterial (e.g. a metal such as palladium) applied to grating 100 usingan atomic layer deposition (ALD) process. Although other processes canbe used to apply a platinum layer to a structure, such processes areunable to uniformly and conformally coat high-aspect ratio structuressuch as grating 100. Thus, ALD processing is critical to formation ofseed layer 106 on grating 100. In one embodiment, seed layer 106 mayhave a thickness (t1) of from about 20 nanometers to about 30nanometers, for example, from about 22 nanometers to about 27nanometers, for example, 24 or 25 nanometers.

Metallic layer 108 may be applied over seed layer 106. Metallic layer108 may be made of an x-ray absorbing material, for example, gold (Au).It is further critical that metallic layer 108 uniformly and conformallycoat grating 100 so that, for example, accurate x-ray results can beachieved using grating 100. In this aspect, metallic layer 108 may bedeposited using an electroplating process as will be described infurther detail below. In one embodiment, metallic layer 108 may have auniform and conformal thickness (t2) of from about 0.1 microns to about1.5 microns, for example, from about 0.2 microns to about 1.2 microns,for example, from 0.25 microns to 1 micron, or from 0.4 microns to 0.6microns.

As previously discussed, in the case of a high aspect-ratio silicongrating such as grating 100 discussed herein, it is difficult touniformly and conformally coat the grating with an x-ray absorbingmaterial such as gold because most processing techniques cause ashadowing effect in which the coating collects at the top of the gratingand blocks off deposition at the bottom of the grating resulting in athinner coating at the bottom than the top. It was, however, surprisingand unexpectedly found that a uniform and conformal coating of ametallic material such as gold can be applied to grating 100 by firstforming seed layer 106 using ALD followed by formation of the metalliclayer 108 using an electroplating process. The critical ALD andelectroplating processing steps for coating grating 100 will now bedescribed in reference to FIG. 2-FIG. 6.

FIG. 2 shows an illustrative process for manufacturing an electroplatedgrating according to one embodiment. Process 200 involves firstproviding a grating (block 202). The grating may be a grating such asgrating 100, for example, a DRIE silicon grating have a highaspect-ratio of 50:1. A conducting seed layer is then applied to thegrating using ALD (block 204). The seed layer may be a seed layer suchas that previously discussed, for example, a platinum seed layer thatuniformly and conformally coats the grating. Next, a metallic layer iselectroplated onto the seed layer (block 206). The metallic layer may bea metallic layer such as the previously discussed metallic layer, forexample, a gold layer that uniformly and conformally coats the grating.

The critical parameters for forming the seed layer using ALD will now bediscussed in more detail. Representatively, once the nonmetallic gratingis cleaned (e.g. using standard UV/ozone cleaning process for 10minutes), it is placed inside an ALD reaction chamber. The grating isoriented to allow the flow of the reactor to be parallel to the trenchfeatures on the grating. In some embodiments, the ALD chamber is a warmwall reactor heated with heating tape. Inside the chamber is a hot stagethat is heated to about 300° C. for the deposition process. A criticalfeature of the ALD chamber is that it is equipped with a back-purgemechanism that promotes the delivery of the platinum ALD precursor (aswell as other solid ALD precursors) into the ALD reaction flow tube.This back-purge flow is incorporated into the major carrier flow when noplatinum ALD precursor is being delivered. When a platinum ALD precursorpulse is being performed, the back-purge is directed to the back end ofthe platinum precursor chamber and helps facilitate the transport of theplatinum ALD precursor vapor (as well as other low vapor pressure ALDprecursor solids) into the reaction flow tube and across the surface ofthe grating. The specific back-purge features of the ALD reactor will bedescribed in more detail in reference to FIG. 3 and FIG. 4.

In one embodiment, the ALD chamber uses nitrogen as the carrier gas. Themajor nitrogen gas flow rate may be, for example, about 100 standardcubic cm per second (sccms) and the minor gas flow rate may be about 20sccms. The pressure in the ALD chamber during the platinum ALD processmay be about 1.5 Torr. Alternating pulses of platinum precursor,(methylcyclopentadienyl)trimethyl platinum, and oxygen may be used togrow the platinum ALD seed layer (block 204). In one embodiment, thepulse and purge cycles of the platinum precursor and oxygen may be 1second pulse, 20 second purge for the platinum precursor and 2 secondpulse and 15 second purge for the oxygen. This sequence producespressure pulses of 30 mTorr of the platinum ALD precursor and 75 mTorrof oxygen. The nominal ALD growth per cycle for the platinum ALD usingthe above-described configuration is about 0.07 nm per ALD cycle. Inanother embodiment, an adhesion layer such as aluminum oxide can beapplied using ALD prior to the platinum layer.

In one embodiment, to apply a platinum seed layer having the desiredthickness, 300 to 375 cycles of ALD are performed. This results in athickness of 22 nm to 27 nm.

Once the seed layer is applied, for example, as described above, themetallic layer is formed over the seed layer. The critical parametersfor forming the metallic layer using electroplating will now bediscussed in more detail. Representatively, the grating having the seedlayer applied thereon is placed within an electroplating chamber. Aswill be described in more detail in reference to FIG. 5, theelectroplating chamber includes an electroplating bath having a laminarflow profile, as opposed to a typical agitated flow, which wasunexpectedly and surprisingly found to facilitate formation of a moreuniform and conformal metallic layer coating on a high aspect-ratiograting such as that disclosed herein. In addition, it was further foundthat by increasing the amount of rest time between forward pulses, amore uniform and conformal metallic layer coating can be achieved.Representatively, the pulse parameters may include an on time of about357 microseconds and an off time of about 96428 microseconds (96.428%).The pulse frequency may be less than 700 Hz. For example, from about 50Hz to about 700 Hz, or from 70 Hz to about 250 Hz, or from about 75 Hzto about 150 Hz, or about 100 Hz. It is noted that this frequency ismuch lower than the typically used electroplating pulse frequency. Itwas surprisingly found, however, that using such a low frequency wasable to accommodate the increased diffusion challenges of the highaspect-ratio gratings. In particular, the modified pulse is capable ofaccounting for kinetic and diffusion limitations in a way that allowsfor uniform plating simultaneously in three directions. In addition, thepulsed current needed for uniformly and conformally coating a highaspect-ratio grating as described herein may be approximately 2 mA/cm².It is noted that the pulsed current readout is usually an average andtherefore much lower than the pulsed current amplitude, which must beaccounted for.

In addition, it was surprisingly and unexpectedly found that modifying aconcentration of certain components within the electroplating chamberbath can facilitate uniform and conformal coating of the highaspect-ratio gratings disclosed herein. Representatively, typically thebath solution includes gold ions and thallium, which is a grain sizereducer. Thallium is typically found within commercially available bathsolutions in an amount of about 80 ppm. It was surprisingly andunexpectedly found that when the thallium concentration was reduced, amore uniform and conformal coating could be achieved. Representatively,in one embodiment, the concentration of thallium used in the bath isless than 80 ppm, for example, less than 60 ppm, or from about 60 ppm toabout 30 ppm, for example, from about 40 ppm to about 50 ppm. Increasingthe gold ion concentration also showed improvements in the depositionmorphology. The adjustments to the deposition chemistry as well as theAC pulse that was applied work synergistically to produce uniform andconformal high aspect ratio coatings.

FIG. 3 shows a schematic cross-sectional view of one embodiment of anatomic layer deposition reactor with a back-purge feature enabled FromFIG. 3, it can be seen that ALD reactor 300 includes an ALD chamber 302,which in some embodiments may be a heated chamber. ALD chamber 302 isdimensioned to hold, for example, a grating 100 as previously discussed.A solid precursor chamber 304, which may also be heated, is connected tothe ALD chamber 302. A solid form of the desired ALD precursor (e.g.platinum) for plating of the grating within the ALD chamber 302 isplaced within the precursor chamber 304. An isolation valve 306, whichisolates and helps control a flow of the precursor from precursorchamber 304 to ALD chamber 302, is positioned between the ALD chamber302 and the precursor chamber 304. In addition, an input port 308 forintroducing a carrier gas (e.g. nitrogen) into the reactor to help carrythe precursor vapors (e.g. oxygen and platinum) to ALD chamber 302 isformed between the isolation valve 306 and ALD chamber 302. A heatedscreen 310 to help vaporize the solid precursor may further be providedbetween the delivery chamber 304 and isolation valve 306. Reactor 300further includes an exhaust output channel 314 at an end of ALD chamber302.

A primary carrier gas (e.g. nitrogen) may be input to carrier gas inputport 308, and in turn ALD chamber 302, through primary carrier gas inputtube 318. In addition, input tube 318 may be connected to the back endof delivery chamber 304 via back-purge tube 322. A back-purge gas valvemanifold 312 and secondary carrier gas input tube 320 are fluidlyconnected to a portion of back-purge tube 322 which is between inputtube 318 and delivery chamber 304. The secondary carrier gas input tube320 may be used to introduce an additional carrier gas into the reactor300. Valve manifold 312 may include a first valve member 330 betweensecondary carrier gas input tube 320 and delivery chamber 304 and asecond valve member 332 between secondary gas input tube 320 and primarycarrier gas input tube 318. In this aspect, valve manifold 312 can beused to control a direction of the additional carrier gas that is inputto the reactor through secondary carrier gas input tube 320.Representatively, when first valve member 330 is open and second valvemember 332 is closed, the carrier gas input through secondary carriergas input tube 320 flows toward delivery chamber 304 (as illustrated bythe arrows). Alternatively, when first valve member 330 is closed andsecond valve member 332 is open, the carrier gas input through secondarycarrier gas input tube 320 flows toward the primary carrier gas inputtube 318 and into ALD chamber 302.

During operation, when the back-purge feature is enabled, the firstvalve member 330 is opened allowing a small amount of the additionalcarrier gas (previously referred to as the minor gas flow) introducedthrough secondary carrier gas input tube 320 to travel into the back endof delivery chamber 304 in the direction of the arrows. This in turnpushes the solid precursor within delivery chamber 304 through screen310 (where it becomes a solid precursor vapor) and past the openisolation valve 306. The pushing of the solid precursor by thisback-purge feature, in combination with the carrier gas (previouslyreferred to as the major carrier gas flow) introduced through input tube318, causes the precursor vapor to travel into ALD chamber 302. It isnoted that due to the diversion of the additional carrier gas intodelivery chamber 304, as opposed to ALD chamber 302, there is a slightpressure drop in ALD chamber 302. This pressure drop creates a pullingeffect, which effectively pulls the precursor vapor into ALD chamber302, and thereby further facilitates transfer of the precursor to ALDchamber 302. It is further noted that since only a small amount of thecarrier gas input into the reactor is diverted through the back-purgefeature, there is no substantial change in the normal carrier gas flow.

FIG. 4 shows a schematic cross-sectional view of the atomic layerdeposition reactor of FIG. 3 with the back-purge feature disabled. Ascan be seen from FIG. 4, when the back-purge feature is disabled, thefirst valve member 330 of the back-purge carrier gas valve manifold 312and the isolation valve 306 are closed to prevent the carrier gas fromtraveling into delivery chamber 304. The second valve member 332,however, is open. In this aspect, the additional carrier gas introducedinto secondary carrier gas input tube 320 travels through tube 322toward input tube 318, where it combines with the carrier gas introducedthrough input tube 318. The combined carrier gases then travel directlyto ALD chamber 302.

FIG. 5 shows a schematic top view of one embodiment of an electroplatingchamber used to manufacture an electroplated grating. From this view, itcan be seen that electroplating chamber 500 includes a tank 502 havingangled walls 504A and 504B connecting sidewall 506A with sidewalls 506Band 506C, respectively. A bath solution inlet tube 508 is positionednear sidewall 506A, between angled walls 504A and 504B. Bath solutioninlet tube 508 may include a plurality of bath solution outlet ports602A, 602B, 602C, 602D, 602E, 602F, 602G, 602H, as illustrated in FIG.6, which is a cross-sectional view of tube 508 of FIG. 5 along line5-5′. Although 8 outlet ports 602A-602G are illustrated, it iscontemplated that any number of ports sufficient to direct a bathsolution toward angled walls 504A and 504B may be provided. Outlet ports602A-602G may direct the bath solution 512 out the sides of the bathsolution inlet tube 508 toward angled walls 504A and 504B. When bathsolution 512 is directed toward angled walls 504A and 504B, angled walls504A and 504B redirect bath solution 512 over the grating/cathode 514mounted to substrate 516 along sidewall 506C and the anode 518 mountedalong sidewall 506B with a laminar flow profile 510A and 510B. It wassurprisingly and unexpectedly found that when bath solution 512 isdirected along the grating/cathode 514 in the laminar flow profile 510Aand 510B, a more conformal and uniform metallic coating is formed on ahigh aspect-ratio grating such as that disclosed herein. Tank 502 mayfurther include sidewall 506D connecting sidewalls 506B and 506C and abath solution outlet tube 524 near sidewall 506D. Bath solution outlettube 524 may be configured to draw bath solution 512 from tank 502 andthrough an associated filter (not shown). It is further to be understoodthat, although not illustrated, tank 502 includes a top wall and abottom wall such that bath solution 512 can be held therein.

In some embodiments, angled walls 504A and 504B form a substantiallychamfered edge connecting sidewall 506A with sidewalls 506B and 506C,respectively. In other words, angled walls 504A and 504B form asubstantially 45 degree angle with respect to what would otherwise be a90 degree angle between sidewall 506A and sidewalls 506B and 506C. Saidanother way, angled wall 504A forms angles 530A and 530B with respectotowalls 506A and 506B, respectively, and angled wall 504B forms angles530C and 530D with respect to walls 506A and 506C, respectively. Angles530A-530D may be greater than 90 degrees, for example, at least 100degrees, or at least 120 degrees, for example, from about 100 degrees toabout 150 degrees, or from about 110 degrees to 145 degrees, or from 125degrees to 135 degrees.

Electroplating chamber 500 may further include a power source 520 (e.g.,an AC power source) configured to provide power via electricalconnections 522A and 522B to anode 518 and grating/cathode 514,respectively.

The following example illustrates the criticality of the electroplatingparameters discussed herein in forming a uniform and conformal coatingof a metallic layer (e.g. gold layer) on a high aspect-ratio silicongrating having a platinum seed layer as previously discussed.

Example I

Conformal gold electroplated coatings are most commonly produced byapplying direct current (DC) to aqueous gold plating chemistries.Initial attempts that used DC deposition to coat a high aspect ratiosilicon (Si) substrate with DRIE gratings resulted in heavy localizedplating on the tops of gratings with minimal plating deep in thetrenches. The high potential required to drive this current in adiffusion limited regime resulted in a high stress deposit and theatomic layer deposition (ALD) platinum (Pt) delaminated from the Si. Thehigh aspect-ratio of the Si gratings restricted the plating in thetrenches and resulted in extremely localized and high current density atthe top of the gratings. This caused dendritic and dull depositappearance.

Based on these results, an alternating current (AC) plating with thepulse that has been used in electrofilling high aspect ratio featureswas tried. In particular, an AC pulse profile of % duty and 700 Hz wasused. The pulse was selected for bottom up filling and showedimprovement over DC; but gold (Au) ion depletion, due to the plating ontop and sides of the gratings, still lead to underplating deeper in thetrenches.

The amount of rest time between forward pulses was therefore increasedto 300 Hz to allow the gold chemistry to reach a concentrationequilibration between deposition times. The length of the pulse was notchanged because prior results showed smooth and uniform grain depositsat this duration. It was found that the increase in rest time improvedthe uniformity of the deposit across the topography. However, there wasstill a thickness gradient in the Au electroplated coating with athicker coating at the top of the grating and a thinner coating towardsthe base of the channel.

Based on this information the rest period was further lengthened byreducing the frequency to 100 Hz. This surprisingly and unexpectedlyresulted in a uniform and highly conformal gold coating with no signs ofdiffusion limitations into the deep Si gratings. It is believed that themodified pulse is capable of accounting for kinetic and diffusionlimitations in a way that allows for uniform plating simultaneously inthree directions. This resulted in a silicon DRIE grating withapproximately 1 micron thick gratings and 4 microns center to centerspacing, being uniformly coated in approximately 1 micron of gold in aperiodic repeat of 1 micron gold, 1 micron silicon, 1 micron gold and 1micron of void space. Because silicon and the void space are transparentto x-rays, the device simulates simply a 1 micron gold grating on a 2micron pitch. The tops and bottoms of the gratings also had a 1 microncoating of gold, but this thin layer was negligible when penetration wasperpendicular.

In the description above, for the purposes of explanation, numerousspecific details have been set forth in order to provide a thoroughunderstanding of the embodiments. It will be apparent however, to oneskilled in the art, that one or more other embodiments may be practicedwithout some of these specific details. The particular embodimentsdescribed are not provided to limit the invention but to illustrate it.The scope of the invention is not to be determined by the specificexamples provided above but only by the claims below. In otherinstances, well-known structures, devices, and operations have beenshown in block diagram form or without detail in order to avoidobscuring the understanding of the description. Where consideredappropriate, reference numerals or terminal portions of referencenumerals have been repeated in the figure to indicate corresponding oranalogous elements, which may optionally have similar characteristics.

It should also be appreciated that reference throughout thisspecification to “one embodiment”, “an embodiment”, “one or moreembodiments”, or “different embodiments”, for example, means that aparticular feature may be included in the practice of the invention.Similarly, it should be appreciated that in the description, variousfeatures are sometimes grouped together in a single embodiment, figure,or description thereof for the purpose of streamlining the disclosureand aiding in the understanding of various inventive aspects. Thismethod of disclosure, however, is not to be interpreted as reflecting anintention that the invention requires more features than are expresslyrecited in each claim. Rather, as the following claims reflect,inventive aspects may lie in less than all features of a singledisclosed embodiment. Thus, the claims following the DetailedDescription are hereby expressly incorporated into this DetailedDescription, with each claim standing on its own as a separateembodiment of the invention.

What is claimed is:
 1. A method for electroplating a nonmetallic grating comprising: providing a nonmetallic grating having an aspect-ratio of from 50:1 to 60:1; performing an atomic layer deposition (ALD) reaction to form a seed layer directly on the nonmetallic grating, wherein the seed layer uniformly and conformally coats the nonmetallic grating such that a thickness of the seed layer is substantially the same along an entire surface of the nonmetallic grating, and wherein performing the ALD reaction comprises: (i) placing the nonmetallic grating in an ALD reactor, the ALD reactor having (a) a back-purge mechanism to facilitate delivery of an ALD precursor vapor across the non-metallic grating, and (b) a pressure of about 1.5 Ton; and (ii) alternating pulses of an ALD precursor and a precursor vapor to grow the seed layer, wherein the pulses are alternated to produce pressure pulses of 30 mTorr of the ALD precursor and 75 mTorr of the precursor vapor and result in a seed layer having a uniform thickness of from 22 nm to 27 nm; and electroplating a metallic layer directly on the seed layer, wherein the metallic layer uniformly and conformally coats the seed layer such that a thickness of the metallic layer is substantially the same along an entire surface of the seed layer, wherein electroplating the metallic layer on the seed layer comprises pulsing an electroplating bath solution comprising thallium across the nonmetallic grating at a pulse frequency of from 50 Hz to 100 Hz, a pulse profile of ¼ duty and a pulse current of 2 mA/cm², and the metallic layer comprises a thickness of from 0.1 microns to 0.6 microns.
 2. The method of claim 1 wherein the aspect-ratio is 60:1.
 3. The method of claim 1 wherein the nonmetallic grating comprises elongated elements having a depth of at least 26 microns and a pitch between each of the adjacent elongated elements is 2 microns or less.
 4. The method of claim 1 wherein the nonmetallic grating comprises silicon.
 5. The method of claim 1 wherein the seed layer comprises palladium.
 6. The method of claim 1 wherein the seed layer comprises platinum.
 7. The method of claim 1 wherein electroplating comprises exposing the nonmetallic grating having the seed layer thereon to an electrical current forward pulse of from 340 to 365 microseconds.
 8. The method of claim 1 wherein electroplating comprises submerging the nonmetallic grating having the seed layer thereon within an electroplating reaction tank, the electroplating reaction tank having outer sidewalls that form chamfered corners, wherein the chamfered corners are dimensioned to generate a laminar flow profile of an electroplating bath solution within the tank, and wherein the electroplating bath solution comprises a thallium concentration of from 40 ppm to 60 ppm.
 9. The method of claim 1 wherein the metallic layer comprises gold.
 10. A method for electroplating a high aspect-ratio silicon grating comprising: providing a silicon substrate having gratings with an aspect-ratio of 60:1; coating the gratings with a conducting seed layer using atomic layer deposition (ALD), wherein the conducting seed layer comprises a same thickness along an entire surface of the gratings, wherein performing ALD comprises: (i) placing the silicon grating in an ALD reactor, the ALD reactor having (a) a back-purge mechanism to facilitate delivery of an ALD precursor vapor across the silicon grating, and (b) a pressure of about 1.5 Torr; and (ii) alternating pulses of an ALD precursor and a precursor vapor to grow the conducting seed layer, wherein the pulses are alternated to produce pressure pulses of 30 mTorr of the ALD precursor and 75 mTorr of the precursor vapor and result in the conducting seed layer having a uniform thickness of 22 nm to 27 nm; and electroplating a gold layer on the conducting seed layer such that the gold layer comprises a same thickness along an entire surface of the conducting seed layer, wherein electroplating the gold layer comprises: (iii) placing the silicon grating having the conducting seed layer thereon into an electroplating chamber, the electroplating chamber comprising outer sidewalls that form chamfered corners dimensioned to produce a laminar flow profile of an electroplating bath across the silicon grating, and wherein the electroplating bath comprises a thallium concentration of from 40 ppm to 60 ppm; and (iv) forming the gold layer on the conducting seed layer by pulsing the electroplating bath across the silicon grating at a pulse frequency of from 50 Hz to 100 Hz, a pulse profile of ¼ duty and a pulse current of 2 mA/cm², and wherein the thickness of the gold layer is from 0.6 microns to 1.5 microns.
 11. The method of claim 10 wherein the gratings have a depth of at least 50 microns and a pitch of less than 5 microns.
 12. The method of claim 10 wherein performing ALD comprises exposing the silicon grating to from 300 to 375 cycles of ALD, wherein the cycles comprise alternating pulse and purge cycles of the ALD precursor and the precursor vapor, wherein each ALD precursor comprises 1 second pulse and 20 second purge and each precursor vapor cycle comprises 2 second pulse and 15 second purge.
 13. The method of claim 10 wherein the chamfered corners form an angle with respect to the outer sidewalls of the electroplating chamber of greater than 90 degrees.
 14. The method of claim 10 further comprising: prior to coating the gratings with a conducting seed layer, using ALD to apply an adhesive layer comprising aluminum oxide to the gratings.
 15. A method for electroplating a nonmetallic grating comprising: providing a nonmetallic grating having an aspect-ratio of 50:1 to 60:1; performing an atomic layer deposition (ALD) reaction to form a seed layer directly on the nonmetallic grating, wherein the seed layer uniformly and conformally coats the nonmetallic grating such that a thickness of the seed layer is substantially the same along an entire surface of the nonmetallic grating, and wherein performing the ALD reaction comprises: (i) placing the nonmetallic grating in an ALD reactor, the ALD reactor having (a) a back-purge mechanism to facilitate delivery of an ALD precursor vapor across the non-metallic grating, and (b) a pressure of about 1.5 Ton; and (ii) alternating pulses of an ALD precursor and a precursor vapor to grow the seed layer, wherein the pulses are alternated to produce pressure pulses of 30 mTorr of the ALD precursor and 75 mTorr of the precursor vapor and result in a seed layer having a uniform thickness of 22 nm to 27 nm; and electroplating a metallic layer directly on the seed layer, wherein the metallic layer uniformly and conformally coats the seed layer such that a thickness of the metallic layer is substantially the same along an entire surface of the seed layer, and wherein electroplating the metallic layer comprises: (iii) placing the nonmetallic grating having the seed layer thereon into an electroplating chamber, the electroplating chamber comprising outer sidewalls that form chamfered corners dimensioned to produce a laminar flow profile of an electroplating bath across the nonmetallic grating, and wherein the electroplating bath comprises a thallium concentration of from 40 ppm to 60 ppm; and (iv) forming the metallic layer on the seed layer by pulsing the electroplating bath across the nonmetallic grating at a pulse frequency of from 50 Hz to 100 Hz, a pulse profile of 1 A duty and a pulse current of 2 mA/cm², and wherein the thickness of the metallic layer is from 0.6 microns to 1.5 microns.
 16. The method of claim 15 wherein the nonmetallic grating comprises elongated elements having a depth of at least 26 microns and a pitch between each of the adjacent elongated elements is 2 microns or less.
 17. The method of claim 15 wherein the nonmetallic grating comprises silicon, the seed layer comprises palladium or platinum, and the metallic layer comprises gold.
 18. The method of claim 15 further comprising: prior to coating the gratings with a conducting seed layer, using ALD to apply an adhesive layer comprising aluminum oxide to the gratings. 